Abstract: In order to simulate overtopping breach of homogeneous earth-rock dams, we carried out experiment in water tank using sand and clay to make mixed materials for dam, and discussed the impact of overtopping breach mode on dam-break parameters. We divided the overtopping breach modes into three kinds: erosion and scour of scarp(M1), erosion and collapse of shear (M2) and erosion and collapse of soak (M3). In the presence of given capacity of reservoir and dam height, maximum breach discharges (Q_p) of different modes are obviously unequal, and Q_p of M2 is the biggest. Breach Critical time(T_C) is referred to as the time from the beginning of overtopping to the developing of breach, and T_C of M2 is the smallest, followed by that of M1 and M3. Breach mode depicts the effects of overtopping flow, initial breach, dam height and dam materials on dam-break process. Besides dam height and capacity of reservoir, breach mode is another important factor for dam-break prediction and disaster assessment.

Key words: earth-rock dam, overtopping breach, breach mode, parameters of breach, disaster assessment